Teachers at the NUT conference staged a small walkout during a speech by the Shadow Education Secretary, Theresa May.

As the Conservative education spokeswoman took to the stage at the annual conference of the National Union of Teachers, in Harrogate, several dozen delegates left the hall in a silent protest.

But after initial heckling - which subsided into low-level groaning and ostentatious reading of newspapers - Ms May delivered a speech attacking the government's proposals to introduce performance-related pay for teachers.

While rejecting proposals for a one-day strike, Ms May called for the scrapping of the government's plans to reward effective teachers with an increase of up to £2,000 per year.

The appraisal system proposed by the government, and strongly opposed by the union, was not a "proper and recognised way for assessing performance".

'Cumbersome'

"The performance related pay scheme being introduced by the government is over-centralised, bureaucratic, cumbersome and expensive," she said.

"It is being pushed through too quickly and there has been inadequate training and too much money spent on administration."

The performance pay system about to be introduced was not really a way of rewarding performance at all, she said, but was a politically expedient way of giving a pay rise to only a proportion of the profession.

Ms May also attacked the number of initiatives being launched by the government, which she said burdened schools with too much bureaucracy and gave teachers an unnecessarily heavy workload.

This increased workload - and the government's "political targets" for improving school test results - were placing too much pressure and stress on schools and individual teachers.

These Department for Education schemes were "centralisation gone mad" and would be overturned under a future Conservative government, said Ms May.